The SAE J845 (2013) Class 1 standard is a certification standard for 360° emitting warning light systems (i.e. so-called “flashing lights”), and includes mechanical, electrical, and optical tests, and is incorporated herein by reference. The SAE J845 (2013) Class 1 standard includes a color test (SAE J578) which involves the use of a spectrophotometer to yield International Commission on Illumination (CIE) (x,y) coordinates based upon the CIE (1931) standard colorimetric system while the light is in its standard mounted position. The SAE J578 test requires that the light emitted by the light system fall within predetermined boundaries depending upon its intended output color; the regions enclosed by these boundaries are referred to herein as “target color regions”. If the light emitted by a light system does not fall within the relevant target color region or shifts out of the target color region during a 30 minute “warm-up” period, it immediately fails the test and therefore cannot be classified under the SAE standard.
FIG. 1 is a graph 100 representing the CIE (1931) standard colorimetric system, with the SAE J578 specifications for red, yellow (amber), green, and blue (including restricted blue and signal blue) target color regions 110, 120, 130, 140 (140A, 140B) respectively, superimposed thereon. FIG. 1 also shows the white color region 170 superimposed on the graph representing the CIE (1931) standard colorimetric system. Thus, the term “white color region”, as used herein, refers to the white color region 170 as shown in FIG. 1. The red, yellow (amber), green, and blue (including restricted blue and signal blue) target color regions 110, 120, 130, 140 (140A, 140B), respectively, are “non-white target color regions”.
For the red target color region 110, the SAE J578 standard requires that the color of light emitted from the device shall fall within the boundaries y=0.335 (yellow boundary) and y=0.980−x (purple boundary), with the remaining boundaries formed by the boundaries of the CIE (1931) color space itself, namely outer curve 150 and lower linear bound 160. This translates to the following set of approximate coordinates defining the boundaries of the red target color region:
XY0.720.2590.730.2650.660.3350.6450.335
For the yellow (amber) target color region 120, the SAE J578 standard requires that the color of light emitted from the device shall fall within the boundaries y=0.390 (red boundary), y=0.790−0.670x (white boundary) and y=x−0.120 (green boundary), with the remaining boundary formed by the outer curve 150 of the CIE (1931) color space itself. This translates to the following set of approximate coordinates defining the boundaries of the yellow (amber) target color region:
XY0.590.390.620.390.560.440.540.42
For the green target color region 130, the SAE J578 standard requires that the color of light emitted from the device shall fall within the boundaries y=0.730−0.730x (yellow boundary), x=0.630y−0.040 (white boundary) and y=0.500−0.500x (blue boundary), with the remaining boundary formed by the outer curve 150 of the CIE (1931) color space itself. This translates to the following set of approximate coordinates defining the boundaries of the green target color region:
XY0.0250.7250.2750.5250.2100.3950.0250.490
The SAE J578 standard divides the blue target color region 140 into a “restricted blue” target color region 140A and a “signal blue” target color region 140B. Light should fall within the restricted blue target color region 140A when recognition of blue as such is necessary; where it is not necessary to identify blue as such, blue light may fall anywhere within the restricted blue target color region 140A or the signal blue target color region 140B. For the restricted blue target color region 140A, the SAE J578 standard requires that the color of light emitted from the device shall fall within the boundaries y=0.070+0.810x (green boundary), x=0.400−y (white boundary) and x=0.130+0.600y (violet boundary), with the remaining boundary formed by the outer curve 150 of the CIE (1931) color space itself. For the signal blue target color region 140B, the SAE J578 standard requires that the color of light emitted from the device shall fall within the boundaries y=0.320 (green boundary), x=0.160 (white boundary), x=0.400−y (white boundary) and x=0.130+0.600 (violet boundary), with the remaining boundaries formed by the border with the restricted blue region 140A and the outer curve 150 of the CIE (1931) color space itself. This translates to the following set of approximate coordinates defining the boundaries of the overall blue target color region:
XY0.140.030.230.170.160.230.160.320.040.32
For the white color region 170, the SAE J578 standard requires that the color of light shall fall within the boundaries x=0.300 (blue boundary), x=0.500 (yellow boundary), y=0.150+0.640x (green boundary), y=0.050+0.750x (purple boundary), y=0.440 (green boundary) and y=0.380 (red boundary). This translates to the following set of approximate coordinates defining the boundaries of the white color region:
XY0.310.280.440.380.500.380.500.440.450.440.310.34
Conventional LED light systems utilize narrow color-band LEDs that typically use two primary material compositions: Aluminum-Indium-Gallium-Phosphide (GaP) and Indium-Gallium-Nitride (GaN). These two compositions yield several very distinct pure colors with narrow bandwidths, which are expressed as the wavelength of the color in nanometers (nm). FIG. 2 is a graph 200 that shows the bandwidths for royal blue 210, blue 220, cyan 230, green 240, yellow (amber) 250, red/orange 260, red 270 and deep red 280; the bandwidths and wavelength ranges for red, red-orange, yellow (amber), green, cyan and blue are also shown in Table 1 below. These wavelengths of pure color define the outer curve 150 of the CIE (1931) color space illustrated by the graph 100 in FIG. 1.
TABLE 1Typical Traditional LED material composition yieldWavelengthMaterial CompositionColorRangeBandwidthAluminum-Indium-Gallium-Red620-645 nm25 nmPhosphideAluminum-Indium-Gallium-Red-Orange610-620 nm10 nmPhosphideAluminum-Indium-Gallium-Yellow580-595 nm15 nmPhosphide(Amber)Indium-Gallium-NitrideGreen520-540 nm20 nmIndium-Gallium-NitrideCyan490-515 nm25 nmIndium-Gallium-NitrideBlue460-485 nm25 nm
White LEDs utilize a phosphor on a blue LED, which converts the blue light into a wide spectrum white output consisting of various wavelengths of light. FIG. 3 is a graph 300 that shows the spectrum outputs for a 5000K-10000K correlated color temperature (CCT) white LED 310, a 3700K-5000K CCT white LED 320 and a 2600K-3700K CCT white LED 330.
GaP and GaN LEDs work well at producing the required color output (i.e. the color of the light falls within the desired target color region), but suffer from certain disadvantages. Blue LEDs do not have very high optical intensity, and GaP LEDs suffer from intensity loss and a larger color shift due to heat at a much higher level than GaN LEDs. FIG. 4 is a graph 400 that shows the thermal degradation of typical pure color GaP, GaN and white LEDs, with lines for yellow (amber) 410, red-orange and red 420, green 430, blue 440 and white 450. The thermal degradation results in the need for multiple LEDs and/or a large (typically metal) heat sink, which will increase the cost of the light system. Also, GaP LEDs typically have a lower forward voltage (2.0V-2.5V) compared to GaN LEDs (3.0V-3.5V), thus requiring different electronic setups to accommodate various colors.
As noted above, white LEDs utilize a phosphor on a blue LED to convert the blue light into a wide spectrum white output consisting of various wavelengths of light. The output can be adjusted to change the color temperature of the white as per the standard blackbody curve by thickening or thinning the phosphor, changing the concentration of the phosphor, or changing the material of the phosphor (typically an yttrium-aluminum-garnet material). The wide output spectrum of white LEDs allows for color filtering techniques (e.g. colored lenses) to be employed.
Similar techniques have been employed to create wider band versions of specific color LEDs, primarily amber and certain greens. These phosphor converted (PC) LEDs have a broader bandwidth than the traditional pure color LEDs; FIG. 5 is a graph 500 showing the spectral output for a lime green PC LED 510 and for a yellow (amber) PC LED 520. This broader spectral output also moved the CIE coordinates of the output of the LED inwardly from standard outer curve 150 of the CIE (1931) color space (FIG. 1), but still allowed the light output from the LED to remain in the target color region specified by the SAE J578 standard. It also improved the thermal degradation of intensity issue with common GaP amber LEDs, and increased the forward voltage to a level that is similar to blue LEDs.
The intensity requirements of SAE J845 fall into two categories: (1) optical intensity and (2) optical power, and are color dependent with white requiring higher outputs than amber and amber requiring higher outputs than both red and blue, as shown in Table 2. The “Angle” column refers to the angle relative to a horizontal line between the light source and a notional viewer; thus “0° (H-V)” represents a notional viewer observing the light source along a horizontal line, i.e. as viewed horizontally from a standard operating orientation of the light system.
TABLE 2Optical Intensity & Optical Power requirements as per SAEJ845 Class 1, for each color at the required test points.AngleWhiteAmberRed & Blue5° Up 76 cd 38 cd19 cd(1800 cd-sec/min) (900 cd-sec/min) (450 cd-sec/min)2.5° Up338 cd169 cd84 cd(8100 cd-sec/min)(4050 cd-sec/min)(2025 cd-sec/min)0° (H-V)676 cd338 cd169 cd (16200 cd-sec/min) (8100 cd-sec/min)(4050 cd-sec/min)2.5° Down338 cd169 cd84 cd(8100 cd-sec/min)(4050 cd-sec/min)(2025 cd-sec/min)5° Down 76 cd 38 cd19 cd(1800 cd-sec/min) (900 cd-sec/min) (450 cd-sec/min)
Optical intensity measures the average flash intensity of a single flash over a known number of flashes, thus yielding the general peak intensity of the light produced by the light system being tested. The optical power portion takes into account the number of flashes and their intensity as it changes during the flash pattern. These two tests not only incorporate the general intensity of the light, but also relate it to the various flash patterns that are present in the light produced by the light system under test. This is important as various patterns have different on times, pulse widths, frequencies, etc. that can affect the optical power of the light output.
As part of the standard test the light systems are allowed to run under normal conditions for 30 minutes before the intensity testing occurs. During this time, the color is still monitored to ensure the color of the light output does not go outside the target color region. The light system is then rotated about its vertical axis, in 10 degree increments, to determine the point having the lowest optical intensity, and then tested from this point. The optical intensity at the test point must fall within 60% of the required minimum to achieve classification. Different minimums are specified for each of Class 1, Class 2 and Class 3 within the SAE J845 standard.